Most TDMA based wireless personal area network (WPAN) or wireless local area network (WLAN) technologies divide a fixed time period into contention free periods and contention periods. For example, in the Institute for Electrical and Electronic Engineers (IEEE) 802.15.3c standard, the fixed time period is called superframe (SF), the contention free period is called CTA (channel time allocation) period, and the contention period is called CAP (contention access period). CTAs are scheduled by a central controller called a PNC (piconet controller) and a CTA is exclusively allocated to a pair of devices. CAP periods are also allocated by the PNC, but the difference from the CTA is that any device can access the medium during CAP periods by contending with each other (e.g., through CSMA/CA). A PNC may be also known as an Access Point (AP) and SF may be also known as Beacon Interval (BI) in the IEEE 802.11 standard. Similarly, CAP may be also known as Contention-Based Period (CBP) and CTA may be also known as Service Period (SP).
Since a CTA is allocated exclusively to a subset of devices in the network, other devices not involved in the communications in that CTA can go to sleep to minimize their energy consumption. However, during CAPs, all the active devices (i.e., the devices which are not in a sleep state) in the network are required to stay awake and cannot go to sleep because any device may try to communicate with any other device, including the PNC, during the CAPs. Therefore, active devices and PNC cannot save power during CAPs.
A similar problem is also present in two other mechanisms. The first is related to CTA truncation and extension. The CTA truncation is a mechanism that releases an unused CTA time period and the CTA extension is a mechanism that extends CTA time if additional time is needed. Since a device that wants to truncate or to extend CTA needs to inform or request to the PNC, the availability of the PNC has to inform the devices. Otherwise, the devices may transmit a CTA truncation or extension messages to the PNC without knowing that the PNC is unavailable.
The second is during the polling period for the dynamic bandwidth allocation mechanism. During the polling period of the dynamic bandwidth allocation, the PNC polls associated devices during unused channel time of a superframe to obtain bandwidth requests from the devices for the purpose of dynamic allocation of the unused channel time. For this period, the PNC needs information whether the devices will be available or not (e.g., device may be in power saving mode). Otherwise, the PNC may transmit polling messages to the devices without knowing that the devices are not available.
Thus, a strong need exists for techniques for device and piconet controller availability notification in wireless personal area and wireless local area networks.
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